Metal organic framework absorbent platforms for removal of CO2 and H2 S from natural gas

ABSTRACT

Provided herein are metal organic frameworks comprising metal nodes and N-donor organic ligands which have high selectivity and stability in the present of gases and vapors including H 2 S, H 2 O, and CO 2 . Methods include capturing one or more of H 2 S, H 2 O, and CO 2  from fluid compositions, such as natural gas.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/564,935 filed on Oct. 6, 2017, which is a National Stage Applicationof PCT Application No. PCT/IB2016/051987 filed on Apr. 7, 2016, whichclaims priority to U.S. Provisional Application No. 62/144,175, filed 7Apr. 2015, which application is incorporated herein by reference.

BACKGROUND

Today there is an increasing global desire to reduce greenhouse gasemissions and develop clean alternative vehicle fuels. Methane (CH₄),the primary component of natural gas (NG), is of particular interest asit is abundant and has lower carbon dioxide (CO₂) emission and moreefficient combustion than other hydrocarbons due its high H/C ratio.Biogases, including landfill gas, are also seen as promising renewableenergy resources, but, like NG, they contain significant amounts ofwater, CO₂, and hydrogen sulfide (H₂S) which must be removed beforebeing transported, stored, and burned as a fuel. For example, NG mustcontain less than 1-2% CO₂ and 4 ppm H₂S to meet fuel gas specificationsfor pipeline transportation. Within many industries, gas dehydration andremoval of CO₂ and H₂S remain some of the most intensive and challengingseparations, in part due to the intolerance of many technologies towater.

Available technologies for refining NG and other biogases are oftencostly, multi-stage processes. Amine scrubbing is a common liquid phasesystem used to remove acid gases such as CO₂ and H₂S from NG. However,stagnant historical operating efficiencies, and the excessive oxidativedegradation, evaporation, and the corrosive nature of the alkanolamineaqueous solutions create a myriad of performance, safety, andenvironmental concerns. Solid, porous material systems, such as zeoliteand metal organic frameworks (MOFs), offer more environmentally friendlyalternatives for CO₂ capture, but require cumbersome, multi-stageprocesses. For example, zeolite has single-species selectivity for CO₂and cyclic adsorption performance in the presence of moisture thatrequire prior dehydration and H₂S removal stages. MOFs, similarly, canbe designed for CO₂ capture but exhibit prohibitively low selectivityfor acid gases such as H₂S. Further, MOFs exhibit low selectivity andcapture at low CO₂ partial pressures.

MOFs generally include porous crystals which are assembled from modularmolecular building blocks, and provide a wide array of advantageousmaterial properties, including high surface area, porosity, stability,and sorption potential. While the available building block options, andcombinations thereof, are virtually limitless, such potential highlightsthe statistical difficulty in identifying and assembling MOFs withdesired and particularized material properties and multi-facetedfunctionality. For example, many MOFs exhibit high selectivity towards aparticular molecular species, but are highly intolerant to water andH₂S.

SUMMARY

In general, this disclosure describes porous metal organic frameworks(MOFs). In particular, this disclosure describes MOFs suitable for thecapture and removal of gases and/or vapors from fluids. It should benoted that although the embodiments of this disclosure are describedwith respect to examples for gas capture, the embodiments describedherein are generally applicable to many fields including gas moleculeseparation, gas storage, catalysis, sensors, drug delivery, rare gasseparation, and proton conductivity.

Embodiments of the present disclosure describe methods of capturingchemical species from a fluid composition comprising contacting a metalorganic framework of formula[M_(a)M_(b)F_(6-n)(O/H₂O)_(w)(Ligand)_(x)(solvent)_(y)]_(z) with a fluidcomposition including at least carbon dioxide and hydrogen sulfide; andcapturing carbon dioxide and hydrogen sulfide from the fluidcomposition; wherein M_(a) is selected from Zn²⁺, Co²⁺, Ni²⁺, Mn²⁺,Zr²⁺, Fe²⁺, Ca²⁺, Ba²⁺, Pb²⁺, Pt²⁺, Pd²⁺, Ru²⁺, Rh²⁺, Mg²⁺, Al⁺³, Fe²⁺,Fe⁺³, Cr²⁺, Cr³⁺, Ru²⁺, Ru³⁺, and Co³⁺; wherein M_(b) is selected fromperiodic groups IIIA, IIIB, IVB, VB, VIB, and VIII; wherein the Ligandis a polyfunctional organic ligand, and x is 1 or more; wherein n is 1,w is 1, x is 2, y is 0 to 4, solvent is a guest molecule, and z is atleast 1.

Embodiments of the present disclosure describe methods of capturingchemical species from a fluid composition comprising contacting a metalorganic framework of formula[M_(a)M_(b)F_(6-n)(O/H₂O)_(w)(Ligand)_(x)(solvent)_(y)]_(z) with a fluidcomposition including at least carbon dioxide and hydrogen sulfide; andcapturing carbon dioxide and hydrogen sulfide from the fluidcomposition; wherein M_(a) is selected from periodic groups IB, IIA,IIB, IIIA, IVA, IVB, VIB, VIIB, and VIII; wherein M_(b) is selected fromAl⁺³, Ga³⁺, Fe⁺², Fe⁺³, Cr²⁺, Cr^(3+,) Ti^(3+,) V^(3+,) V⁵⁺, Sc³⁺, In³⁺,Nb⁵⁺, and Y³⁺; wherein the Ligand is a polyfunctional organic ligand,and x is 1 or more; wherein n is 1, w is 1, x is 2, y is 0 to 4, solventis a guest molecule, and z is at least 1.

The details of one or more examples are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages will be apparent from the description and drawings, and fromthe claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate non-limiting example embodiments ofthe invention.

FIG. 1A illustrates a method for capturing one or more chemical speciesfrom a fluid composition via a metal organic framework, according to oneor more embodiments of this disclosure.

FIG. 1B illustrates a multicolumn pressure-temperature swing adsorption(PTSA) method for capturing one or more chemical species from a fluidcomposition via a metal organic framework, according to one or moreembodiments of this disclosure.

FIG. 2 illustrates a method of fabricating a metal organic framework,according to one or more embodiments of the disclosure.

FIG. 3A illustrates a schematic of an inorganic chain, according to oneor more embodiments of this disclosure.

FIG. 3B illustrates a schematic view of a metal organic framework,according to one or more embodiments of this disclosure.

FIG. 4A illustrates powder X-ray diffraction data of a metal organicframework, according to one or more embodiments of this disclosure.

FIG. 4B illustrates powder X-ray diffraction data of a metal organicframework, according to one or more embodiments of this disclosure.

FIG. 5A illustrates isotherm data for various metal organic frameworks,according to one or more embodiments of this disclosure.

FIG. 5B illustrates isotherm data for various metal organic frameworks,according to one or more embodiments of this disclosure.

FIG. 5C illustrates isotherm data for a metal organic framework,according to one or more embodiments of this disclosure.

FIG. 6 illustrates a block flow diagram of sequence of tests foradsorption column breakthrough studies to evaluate the performances ofthe materials in temperature swing cyclic (TSR) and vacuum swingregeneration (VSR) modes using CO2/H2S/CH4:5/5/90 mixture, according toone or more embodiments of this disclosure.

FIG. 7 illustrates a graphical view of column breakthrough test ofCO₂/H₂S/CH₄ with 10 cm³/min flow rate on NiAlF₅O(pyrazine)₂ at 25° C. (1bar) using TSR mode, according to one or more embodiments of thisdisclosure.

FIG. 8 illustrates a graphical view of column breakthrough tests ofCO₂/H₂S/CH₄ with 10 cm³/min flow rate on NiAlF₅O(pyrazine)₂ at 25° C.and 50° C. (1 bar) respectively (effect of adsorption temperature onretention time), according to one or more embodiments of thisdisclosure.

FIG. 9 illustrates a graphical view of column breakthrough tests ofCO₂/H₂S/CH₄ with 10 cm³/min flow rate on NiAlF₅O(pyrazine)₂ at 50° C. (1bar) after activation at different temperatures (effect of adsorptiontemperature on retention time of different gases), confirming therecyclability of the material, according to one or more embodiments ofthis disclosure.

FIG. 10 illustrates a graphical view of comparison of retention time ofCO₂ and H₂S for studied materials during column breakthrough tests at25° C. (1 bar) after optimal activation of the samples (gas mixtureCO₂/H₂S/CH₄ (5/5/90) with 10 cm³/min flow rate was used for theexperiments), according to one or more embodiments of this disclosure.

FIG. 11 illustrates a graphical view of comparison of retention time ofCO₂ and H₂S for studied materials during column breakthrough tests at50° C. (1 bar) after optimal activation of the samples (gas mixtureCO₂/H₂S/CH₄ (5/5/90) with 10 cm³/min flow rate was used for theexperiments), according to one or more embodiments of this disclosure.

FIG. 12 illustrates a graphical view of comparison of retention time ofCO₂ and H₂S for studied materials during column breakthrough tests at25° C. and 50° C. (1 bar) respectively after optimal activation of thesamples (gas mixture CO₂/H₂S/CH₄ (5/5/90) with 10 cm³/min flow rate wasused for the experiments), according to one or more embodiments of thisdisclosure.

FIG. 13 illustrates a graphical view of comparison of retention time ofCO₂ and H₂S for studied materials during column breakthrough tests at25° C. after optimal activation and 25° C. activation of the samplesrespectively (gas mixture CO₂/H₂S/CH₄ (5/5/90) with 10 cm³/min flow ratewas used for the experiments) and comparison describes compatibility ofthe studied materials for Vacuum Swing Regeneration (VSR) at 25° C.,according to one or more embodiments of this disclosure.

FIG. 14 illustrates a graphical view of comparison of retention time ofCO₂ and H₂S for studied materials during column breakthrough tests at50° C. after optimal activation and 50° C. activation of the samplesrespectively (gas mixture CO₂/H₂S/CH₄ (5/5/90) with 10 cm³/min flow ratewas used for the experiments) and comparison describes compatibility ofthe studied materials for Vacuum Swing Regeneration (VSR) at 50° C.,according to one or more embodiments of this disclosure.

FIG. 15 illustrates a graphical view of comparison of retention time ofCO₂ and H₂S for studied materials during column breakthrough tests at25° C. with fresh samples and samples after five breakthrough cyclesrespectively after optimal activation (gas mixture CO₂/H₂S/CH₄ (5/5/90)with 10 cm³/min flow rate was used for the experiments) and comparisondescribes recyclability of the studied materials, according to one ormore embodiments of this disclosure.

DETAILED DESCRIPTION

Provided herein are a series of highly stable and highly tunable MOFswith high affinity and stability to water and H₂S. Such qualities allowfor efficient and cost effective methods for dehydrating gases, vapors,and solvents capable of replacing many cumbersome and expensiveindustrial processes. Further, this novel series of MOFs can be designedwith a variety of pore sizes and assembled with and without open-metalsites, affording tunable properties for a variety of separationapplications. For example, the MOFs provided herein can capture chemicalspecies from fluid compositions under conditions and in the presence ofchemical species which render known gas capture technologiesinefficient, impracticable, or inoperable. In particular, the MOFsprovided herein can capture one or more of H₂O, CO₂ and H₂S from a fluidcomposition, such as natural gas, while maintaining high structuralintegrity during both adsorption and desorption.

The present invention is described with reference to the attachedfigures, wherein like reference numerals are used throughout the figuresto designate similar or equivalent elements. The figures are not drawnto scale and they are provided merely to illustrate the invention.Several aspects of the invention are described below with reference toexample applications for illustration. It should be understood thatnumerous specific details, relationships, and methods are set forth toprovide an understanding of the invention. One skilled in the relevantart, however, will readily recognize that the invention can be practicedwithout one or more of the specific details or with other methods. Inother instances, well-known structures or operations are not shown indetail to avoid obscuring the invention. The present invention is notlimited by the illustrated ordering of acts or events, as some acts mayoccur in different orders and/or concurrently with other acts or events.Furthermore, not all illustrated acts or events are required toimplement a methodology in accordance with the present invention.

As used herein, “fluids” can refer to a gas, liquid, or combinationthereof. A gas or liquid can include one or more components. Forexample, a fluid can include a gas stream comprising CO₂, H₂S and watervapor.

As used herein, “refining” refers to removing one or more unwantedcomponents or separating one or more components from remainingcomponents of a composition, such as a fluid. For example, refining caninclude removing a fraction of H₂S from a fluid, such as natural gas.

As used herein, “poly-functional” refers to the characteristic of havingmore than one reactive or binding sites. For example, a poly-functionalligand can attach to a metal ion in multiple ways, bridge multiple metalions, or combinations thereof. Specifically, pyrazine is apoly-functional ligand.

Gas storage and separation using porous materials has experiencedsignificant development in recent years in various industrialapplications related to energy, environment, and medicine. Among porousmaterials, metal organic frameworks (MOFs) are a versatile and promisingclass of crystalline solid state materials which allow porosity andfunctionality to be tailored towards various applications. MOF crystalchemistry uses a molecular building block (MBB) approach that offerspotential to construct MOFs where desired structural and geometricalinformation are incorporated into the building blocks prior to theassembly process.

Generally, MOFs comprise a network of nodes and ligands, wherein a nodehas a connectivity capability at three or more functional sites, and aligand has a connectivity capability at two functional sites each ofwhich connect to a node. Nodes are typically metal ions or metalcontaining clusters, and, in some instances, ligands with nodeconnectivity capability at three or more functional sites can also becharacterized as nodes. In some instances, ligands can include twofunctional sites capable of each connecting to a node, and one or moreadditional functional sites which do not connect to nodes within aparticular framework. A MBB can comprise a metal-based node and anorganic ligand which extrapolate to form a coordination network. Suchcoordination networks have advantageous crystalline and porouscharacteristics affecting structural integrity and interaction withforeign species (e.g., gases). The particular combination of nodes andligands within a framework will dictate the framework topology andfunctionality. While essentially limitless combinations of nodes andligands exist, to date, very few MOF materials are H₂S stable whichconsequently preclude their use in gas separation.

As disclosed in co-owned U.S. Application No. 62/044,928, a series ofisoreticular MOFs with periodically arrayed hexafluorosilicate (SiF₆)pillars, called SIFSIX-2-Cu-i and SIFSIX-3-Zn, SIFSIX-3-Cu andSIFSIX-3-Ni showed particularly high CO₂ selectivity and capture. Theseproperties in SIFSIX-3-M materials suggest broad applications from ppmlevel CO₂ removal to bulk CO₂ separation. However, with the exception ofSIFSIX-3-Ni, the SIFSIX-3-M materials were not tolerant to H₂S. Andalthough these materials exhibit high structural structurally in thepresence of CO₂, extensive exposure of all SIFSIX-3-M materials tomoisture detrimentally induces a phase change and the formation of new2D stable materials. These 2D materials exhibit relatively unalteredselectivity but diminished CO₂ uptake. This indicates that theSIFSIX-3-M materials series is not sufficiently robust to handle CO₂ andH₂S capture in most critical applications throughout the oil and gas andrenewable fuels industries, especially in applications which bring thematerials into contact with moisture.

Provided herein are novel functionalized MOFs suitable for the removalof acid gases, particularly CO₂ and H₂S, which additionally exhibit highwater vapor tolerance and stability over thousands of cycles. These MOFseliminate the safety, efficiency, and environmental concerns associatedwith amine scrubbing techniques while providing high selectivity towardacid gases and negligible uptake of other components, including CH₄. Theproposed class of materials will permit NG and biofuels refiningapproaches based on simultaneous removal of CO₂, H₂S and water vapor.The benefits of this innovative approach include the following: (i) noenvironmental and safety hazards germane to amine scrubbing (ii) nopreliminary separate desulfurization is necessary (iii) no separate gasdrying is needed, and (iv) no compression-decompression/cooling of NG isrequired. Further, the MOFs provided herein offer exceptional thermaland mechanical stability, particularly during adsorption/desorption.

MOFs as provided herein comprise one or more MBBs. Generally, a MBB, ora network of MBBs, can be represented by the formula[(node)_(a)(ligand)_(b)(solvent)_(c)]_(n), wherein n represents thenumber of molecular building blocks. Solvent represents a guest moleculeoccupying pores within the MOF, for example as a result of MOFsynthesis, and can be evacuated after synthesis to provide a MOF withunoccupied pores. In one example, an evacuated MOF can be subsequentlyenriched with a guest molecule compatible with the MOF framework and/orpores for a particular purpose (e.g., to outfit the MOF for use as asensor). In other embodiments, guest molecules can include adsorbedgases, such as H₂S. While guest molecules can impart functionality ontoa MOF, such are not a permanent fixture of the MOF. Accordingly, thevalue of c can vary down to zero, without changing the definitionalframework of the MOF. Therefore in many instances, MOFs as providedherein will be defined as [(node)_(a)(ligand)_(b)]_(n), withoutreference to a solvent or guest molecule component.

In some embodiments herein, MOFs can be characterized by the formula[(node)_(a)(ligand)_(b)(solvent)_(c)]_(n). A non-limiting list ofsolvents can include one or more of H₂O, DMF, and DEF. In someembodiments, solvent can include a chemical species present afterfabrication of the MOF. In some embodiments, solvent can include afunctionalizing guest molecule, such as water, DMF, and DEF. Someembodiments herein comprise a porous, uninhabited MOF characterized bythe formula [(node)_(a)(ligand)_(b)]_(n), wherein node comprises,generally, M_(a)M_(b)F_(x)O_(y)(H₂O)_(z). In some embodiments, M_(a)comprises elements selected from periodic groups IB, IIA, IIB, IIIA,IVA, IVB, VIB, VIIB, or VIII. In some embodiments, M_(b) compriseselements selected from periodic groups IIIA, IIIB, IVB, VB, VIB, orVIII. In some embodiments, M_(a) comprises elements selected fromperiodic groups IB, IIA, IIB, IIIA, IVA, IVB, VIB, VIIB, or VIII andM_(b) comprises elements selected from periodic groups IIIA, IIIB, IVB,VB, VIB, or VIII. In some embodiments, M_(a) can comprise one of thefollowing cations: Cu²⁺, Zn²⁺, Co²⁺, Ni²⁺, Mn²⁺, Zr²⁺, Fe²⁺, Ca²⁺, Ba²⁺,Pb²⁺, Pt²⁺, Pd²⁺, Ru²⁺, Rh²⁺, Cd²⁺, Mg⁺², Al⁺³, Fe⁺², Fe⁺³, Cr²⁺, Cr³⁺,Ru²⁺, Ru³⁺ and Co³. In some embodiments, M_(b) can be one of thefollowing Al⁺³, Fe⁺², Fe⁺³, Cr²⁺, Cr³⁺, Ti³⁺, V³⁺, V⁵⁺, Sc³⁺, In³⁺,Nb⁵⁺, Y³⁺. In some embodiments, M_(a) can comprise one of the followingcations: Cu²⁺, Zn²⁺, Co²⁺, Ni²⁺, Mn²⁺, Zr²⁺, Fe²⁺, Ca²⁺, Ba²⁺, Pb²⁺,Pt²⁺, Pd²⁺, Ru²⁺, Rh²⁺, Cd²⁺, Mg⁺², Al⁺³, Fe⁺², Fe⁺³, Cr²⁺, Cr³⁺, Ru²⁺,Ru³⁺ and Co³; M_(b) can be one of the following Al⁺³, Fe⁺², Fe⁺³, Cr²⁺,Cr³⁺, Ti^(3+,) V³⁺, V⁵⁺, Sc³⁺, In³⁺, Nb⁵⁺, Y³⁺. In such embodiments, theligand can be any bi-functional N-donor linkers based on monocyclic orpolycyclic group (aromatic or not).

In some embodiments, a ligand can comprise a polydentate, orpoly-functional ligand, such as a bi-functional ligand, a tri-functionalligand, or ligands with four or more functional sites. In someembodiments, a ligand can comprise an N-donor linker. In someembodiments a ligand can comprise a poly-functional ligand. In someembodiments, a ligand can comprise a plurality of N-donor functionalgroups. In some embodiments, a ligand can comprise a monocyclic orpolycyclic group structure, wherein the cyclic groups can be aromatic ornon-aromatic. In some embodiments, a ligand can comprise anitrogen-containing monocyclic or polycyclic group structure. In someembodiments, a ligand can comprise a nitrogen-containing heterocyclicligand, including pyridine, pyrazine, pyrimidine, pyridazine, triazine,thiazole, oxazole, pyrrole, imidazole, pyrazole, triazole, oxadiazole,thiadiazole, quinoline, benzoxazole, benzimidazole, and tautomersthereof.

Some embodiments of suitable MOFs can be represented by the followinggeneral formula: [M_(a)M_(b)F_(x)(O/H₂O)_(z)(Ligand)₂]_(n) wherein M_(a)can be one of the following cations: Cu²⁺, Zn²⁺, Co²⁺, Ni²⁺, Mn²⁺, Zr²⁺,Fe²⁺, Ca²⁺, Ba²⁺, Pb²⁺, Pt²⁺, Pd²⁺, Ru²⁺, Rh²⁺, Cd²⁺, Mg⁺², Al⁺³, Fe⁺²,Fe⁺³, Cr²⁺, Cr³⁺, Ru²⁺, Ru³⁺ and Co³; M_(b) can be one of the followingAl⁺³, Fe⁺², Fe⁺³, Cr²⁺, Cr³⁺, Ti³⁺, V³⁺, V⁵⁺, Sc³⁺, In³⁺, Nb⁵⁺, Y³⁺; andthe ligand can be any bi-functional N-donor linkers based on monocyclicor polycyclic group (aromatic or not).

The utility of MOFs such as those provided herein are highly dependentupon the framework's structural features such as structural strength,density, functionality, pore aperture dimensions, pore dimensions, theratio of pore aperture dimensions to pore dimensions, poreaccessibility, and the presence of a plurality of pore dimensions and/orpore aperture dimensions (e.g., a poly-porous MOF). The originality ofthis new class of crystalline porous materials is based, in part, on thefact that the shape of cavities, (i.e. square or rectangle basedchannels), is controlled from a structural point of view usingappropriate cations and organic linkers. The novel MOF architecturesdisclosed herein offer a novel improvement on some MOF architectures byreplacing silicon components with other metals, such as Al³⁺, Fe²⁺,Fe³⁺, V³⁺, V⁴⁺, V⁵⁺, Nb⁵⁺, to afford highly stable materials with orwithout open metals sites. In some embodiments, the use of specificcations, such as Al⁺³, Fe⁺², Fe⁺³, Cr²⁺, Cr^(3+,) Ti^(3+,) V^(3+,) V⁵⁺,Sc³⁺, In³⁺, Y³⁺, in M_(b) site positions can introduce open-metal siteswithin the channels that enhance properties of gas capture.

These, and other features, collaborate to achieve MOFs with highaffinity and stability to water and H₂S. Additionally, the novel seriesof MOFs structures disclosed herein can be designed with a variety ofpore sizes and/or open-metal sites which afford tunable properties for avariety of gas/vapor/solvent separation applications. Tuning, in someembodiments, can include modification of the organic and/or inorganiccomponents of the MOF. For example, lighter metal-based clusters can beused to lower the framework density and increase the relative wt. % ofcaptured CO₂ and/or H₂S. Further, the MOF platforms as provided hereinallow for an unprecedented high degree of tuning control at themolecular level, allowing the size and shape of channels within a MOFarchitecture to be rigorously controlled and adapted to specificseparation of numerous gases, beyond CO₂ and H₂S.

In some embodiments, a representativeM_(a)M_(b)F_(w)O_(x)(H₂O)_(y)(Ligand)_(z) MOF structure can include a NiM_(a) constituent, an M_(b) constituent group selected from one of Al,Fe, V, or Nb, and a Ligand comprising a pyrazine constituent group,wherein x can vary from 0 to 10. All such embodiments offer highaffinity and stability to water vapor and H₂S, unlike the Cu andZn-based analogues of SIFSIX-3-M materials made with Si. In someembodiments a MOF characterized by the formula[M_(a)M_(b)F_(6-n)(O/H₂O)_(n)(Ligand)₂(solvent)_(x)]_(n) wherein M_(a)equals Ni, M_(b) equals Al, Fe, V or Nb, and ligand equals pyrazine, thepore size (channel size) of the resulting MOF can be about 3.3 Å toabout 3.8 Å. In some embodiments, the channels are square/rectangular.In the same or in an alternative embodiment, a MOF can have a specificsurface area of about 250 m²/g to about 500 m²/g. In either of the sameMOFs or in an alternative embodiment, a MOF can have a pore volume ofabout 0.1 cm³/g to about 0.25 cm³/g. In a different embodiment, a moreelongated ligand can provide an analogous MOF with much higher porosity.

FIG. 1A illustrates a method 100 for capturing 120 one or more chemicalspecies from a fluid composition 110 via a first MOF 105. A method 100for capturing 120 one or more chemical species from a fluid composition110 can comprise contacting 115 a metal organic framework 105characterized by the formula[M_(a)M_(b)F_(6-n)(O/H₂O)_(w)(Ligand)_(x)(solvent)_(y)]_(z) with a fluidcomposition 110. Fluid composition 110 can comprise two or more chemicalspecies. Fluid composition 110 can comprise natural gas. In oneembodiment, fluid composition 110 comprises one or more of carbondioxide, water, and hydrogen sulfide. In such an embodiment, fluidcomposition 110 can further comprise methane.

Method 100 can further comprise capturing 120 one or more chemicalspecies from the fluid composition 110. Capturing 120 can comprisecapturing one or more of carbon dioxide, water, and hydrogen sulfide.Capturing 120 can comprise capturing two or more of carbon dioxide,water, and hydrogen sulfide. In some embodiments, capturing 120comprises physical adsorption of the one or more captured chemicalspecies by the first MOF 105. In some embodiments, capturing 120comprises chemisorption of the one or more captured chemical species bythe first MOF 105. Chemisorption can occur by one or more capturedchemical species chemically interacting with one or more open metalsites of the first MOF 105. In other embodiments, capturing 120comprises physical adsorption and chemisorption of the one or morecaptured chemical species by the metal organic framework. Capturing 120can comprise wholly or partially containing a chemical species within apore of a MOF. In some embodiments, capturing 120 consists ofchemisorption. In some embodiments, capturing 120 consists of physicaladsorption. Capturing 120 can occur in a capturing environment. Acapturing environment can comprise one or more of ambient temperature orpressure. A capturing environment can comprise a pressurize-controlledvessel. A capturing environment can comprise a temperature-controlledvessel. A capturing environment can comprise a pressure andtemperature-controlled vessel. A capturing environment can comprise thefirst MOF 105 in the form of a fixed bed, a packed column, orcombinations thereof.

Capturing 120 can further comprise changing the temperature of thecapture environment to alter the affinity of one or more chemicalspecies for the MOF. Similarly, capturing 120 can further comprisechanging the pressure of the capture environment to alter the affinityof one or more chemical species for the MOF. Additionally, capturing 120can further comprise changing the temperature and pressure of thecapture environment to alter the affinity of one or more chemicalspecies for the MOF. In such embodiments, the chemical species canparticularly include carbon dioxide, water, and hydrogen sulfide.

Method 100 can further comprise desorbing one or more of carbon dioxide,water, and hydrogen sulfide from the MOF. Method 100 can furthercomprise desorbing two or more of carbon dioxide, water, and hydrogensulfide from the MOF. Desorbing can occur in a desorbing environment. Adesorbing environment can comprise one or more of ambient temperature orpressure. A desorbing environment can comprise a pressurize-controlledvessel. A desorbing environment can comprise a temperature-controlledvessel. A desorbing environment can comprise a pressure andtemperature-controlled vessel. While a MOF can capably capture a numberof gaseous or vapor phase species, a relative affinity hierarchy will,in principle, exist among those species. In embodiments where method 100comprises desorbing two or more of carbon dioxide, water, and hydrogensulfide from the MOF, carbon dioxide, water, and hydrogen sulfide can besequentially desorbed in descending order of affinity. In a particularembodiment, H₂S is desorbed first, CO₂ is desorbed second, and H₂O isdesorbed last.

In some embodiments, the relative affinity hierarchy of chemical speciescan be manipulated. Accordingly, desorbing can further comprise changingthe temperature of the desorbing environment to alter the affinity ofone or more chemical species for the MOF. Similarly, desorbing canfurther comprise changing the pressure of the desorbing environment toalter the affinity of one or more chemical species for the MOF.Additionally, desorbing can further comprise changing the temperatureand pressure of the desorbing environment to alter the affinity of oneor more chemical species for the MOF. In such embodiments, the chemicalspecies can particularly include carbon dioxide, water, and hydrogensulfide. In some embodiments, one or more of capturing and desorbing iseffected by multicolumn pressure-temperature swing adsorption.Multicolumn pressure-temperature swing adsorption is known in the art.

Method 100 can further comprise contacting 115 the fluid composition 110with a second MOF, characterized by the formula[M_(c)M_(d)F_(6-n)(O/H₂O)_(w)(Ligand)_(x)(solvent)_(y)]_(z). In someembodiments, the second MOF is different from the first MOF 105. In someembodiments, contacting 115 the fluid composition with the first MOF 105and the second MOF occurs separately. In some embodiments, contacting115 the fluid composition with the first MOF 105 and the second MOFoccurs sequentially. In some embodiments, contacting 115 the fluidcomposition with the first MOF 105 and the second MOF occurssimultaneously. Method 100 can further comprise contacting 115 the fluidcomposition 110 with three or more MOFs.

In some embodiments, the first MOF comprises one or more MOFs asprovided herein. For example, the first MOF can comprise an MOFcharacterized by the formula[NiN_(b)F_(6-n)(O/H₂O)_(w)(Ligand)_(x)(solvent)_(y)]_(z). In someembodiments the second MOF comprises one or more MOFs as providedherein. For example, the second MOF can comprise an MOF characterized bythe formula [NiM_(d)F_(6-n)(O/H₂O)_(w)(Ligand)_(x)(solvent)_(y)]_(z)wherein M_(d) comprises Al⁺³, Fe⁺², or Fe⁺³. In some embodiments, theMOF is characterized by the formula[NiN_(b)F_(6-n)(O/H₂O)_(w)(Ligand)_(x)(solvent)_(y)]_(z) and the secondMOF is characterized by the formula[NiM_(d)F_(6-n)(O/H₂O)_(w)(Ligand)_(x)(solvent)_(y)]_(z) wherein M_(d)comprises Al⁺³, Fe⁺², or Fe⁺³.

FIG. 1B illustrates a method 101 for removing one or more of carbondioxide, water, and hydrogen sulfide from natural gas via a MOF.Removing can one or more of carbon dioxide, water, and hydrogen sulfidefrom natural gas can occur simultaneously. Removing can one or more ofcarbon dioxide, water, and hydrogen sulfide from natural gas can occurseparately. Removing can occur in a multicolumn pressure-temperatureswing adsorption (PTSA) system. In one embodiment, the MOF comprises oneof Ni(Al/Fe/V/Nb)F₅(O/H₂O)_(x)(pyrazine)₂(solvent)_(x). In anotherembodiment, the MOF comprises two or more ofNi(Al/Fe/V/Nb)F(O/H₂O)_(x)(pyrazine)₂(solvent)_(x).

MOFs as provided herein can be fabricated using a solvo(hydro)thermalsynthetic procedure. As shown in FIG. 2, a method for fabricating 200 aMOF 230 can include combining 205 reactants. Reactants can include oneor more of a fluorhydric acid solution 206 with a Ni²⁺ source 207, asecond metal source 208, and a solvent 209 to form a mixture 210. A Ni²⁺source 207 can include one or more of nickel nitrate, hydrated nickelnitrate, nickel chloride, hydrated nickel chloride, nickel fluoride,hydrated nickel fluoride, nickel oxide, or hydrated nickel oxide. Thesecond metal source 208 can include an Al⁺³ source, an Fe⁺² source, anFe⁺³ source, a Cr²⁺ source, a Cr³⁺ source, a Ti³⁺ source, a V³⁺ source,a V⁵⁺ source, a Sc³⁺ source, an In³⁺ source, a Nb⁵⁺ source, or a Y³⁺source, for example. These, metals can be in the form of nitrates,hydrated nitrates, chlorides, hydrated chlorides, fluorides, hydratedfluorides, oxides, hydrated oxides, and combinations thereof. Thesolvent 209 can include one or more of H₂O, dimethylformamide (DMF), anddiethylformamide (DEF).

The method for fabricating 200 can further comprise to reacting 215 themixture 210, sufficient to form a reacted mixture 220. Reacting 215 caninclude contacting the fluorhydric acid solution 206, the Ni²⁺ source207, the second metal source 208, and the solvent 209. Reacting 215 canfurther comprise stirring or agitating the mixture 210, or heating themixture 210. Heating the mixture 210 can comprise heating to atemperature between about 80° C. to about 200° C. The reacted mixture220 can be further processed 225 to provide a fabricated MOF 230.Processing 220 can include one or more of filtering the reacted mixture220, rinsing the reacted mixture 220 with water, removing excessreactants from the reacted mixture 220. In some embodiments, guestmolecules are optionally evacuated from a fabricated MOF 230. Guestmolecules can include solvent guest molecules, or derivatives thereof.

One MOF synthesis strategy provided herein comprises linking inorganicchains using appropriate N-donor based linkers to deliberately generatechannels along one crystallographic direction. The inorganic chains arebuilt up from the trans-connection between M_(a)N₄F₂ and M_(b)F₄(H₂O)₂octahedra or between M_(a)N₄F₂ and M_(b)F₅(H₂O) octahedra or betweenM_(a)N₄F₂ octahedra and M_(b)F₅(O) octahedra. FIG. 3A illustrates anexample of an inorganic chain, built up from M_(a)N₄F₂ and M_(b)F₅(H₂O)octahedra. The resulted inorganic chains are linked to each other usingbi-functional N-donor organic ligands, thereby generating channels withdifferent sizes and shapes depending on the nature of the organiclinker. FIG. 3B illustrates a schematic view of one embodiment of a MOFcomprising a NiN_(b)F₅O(pyrazine)₂ structure, viewed along the c-axis.

In one embodiment, a representative M_(a)M_(b)F_(x)O_(y)(Ligand)₂ MOFstructure can include a Ni M_(a) constituent, a Nb M_(b) constituentgroup, and a Ligand comprising a pyrazine constituent group. FIG. 4Aillustrates powder X-ray diffraction data of this MOF, characterized bythe formula NiN_(b)F₅O(pyrazine)₂(solvent)_(x), confirming the highstability of the MOF in the presence of water. FIG. 4B illustratespowder X-ray diffraction data of this MOF, confirming the high stabilityof the MOF in the presence of H₂S.

FIGS. 5A-C illustrates the broad potential for MOFs characterized by theformula Ni(Al/Fe/V/Nb)F(O/H₂O)_(x)(pyrazine)₂(solvent)_(x), and variantsthereof. FIG. 5A illustrates CO₂ isotherms at 298 K for each of thesefour MOFs, which show extremely high sorption of CO₂ across all testpressures (0-1 bar), FIG. 5B illustrates H₂S isotherms at 298K for threeMOFs characterized by the formulaNi(Al/Fe/V)F₅(O/H₂O)_(x)(pyrazine)₂(solvent)_(z), which shows across alltest pressures (0-1, wherein 1 corresponds to a 0.1 H₂S partialpressure).

FIG. 5C Illustrates H₂O sorption isotherms at 298K forNi(Al)F₅(O/H₂O)_(x)(pyrazine)₂(solvent)_(z), indicating the highsuitability of this MOF for gas dehydration applications, among others.These results demonstrate the value of the MOF embodiment characterizedby the formula Ni(Al/Fe/V/Nb)F(O/H₂O)_(x)(pyrazine)₂(solvent)_(x) as aplatform for refining a number of valuable hydrocarbon gases and fluids,including methane, natural gas, and biogas. The exemplary performanceand properties of the Nb⁵⁺ based MOFs disclosed herein are notablyachieved in spite of having no open metal sites. These and other resultscan be expected in similar other embodiments, with or without open metalsites, such as MOF structure characterized by the formulaNiM_(b)F₅O(pyrazine)₂, wherein M_(b) can be one of the following Al⁺³,Fe⁺², Fe⁺³, Cr²⁺, Cr^(3+,) Ti^(3+,) V^(3+,) V⁵⁺, Sc³⁺, In³⁺, Nb⁵⁺, Y³⁺.These and other results can be expected in similar other embodiments,with or without open metal sites, such as MOF structure characterized bythe formula M_(a)N_(b)F₅O(pyrazine)₂, wherein M_(a) can be one of thefollowing cations: Cu²⁺, Zn²⁺, Co²⁺, Ni²⁺, Mn²⁺, Zr²⁺, Fe²⁺, Ca²⁺, Ba²⁺,Pb²⁺, Pt²⁺, Pd²⁺, Ru²⁺, Rh²⁺, Cd²⁺, Mg⁺², Al⁺³, Fe⁺², Fe⁺³, Cr²⁺, Cr³⁺,Ru²⁺, Ru³⁺. These and other results can also be expected in similarother embodiments, with or without open metal sites, such as MOFstructure characterized by the formula M_(a)(Al/Fe/V)F₅O(pyrazine)₂,wherein M_(a) can be one of the following cations: Cu²⁺, Zn²⁺, Co²⁺,Ni²⁺, Mn²⁺, Zr²⁺, Fe²⁺, Ca²⁺, Ba²⁺, Pb²⁺, Pt²⁺, Pd²⁺, Ru²⁺, Rh²⁺, Cd²⁺,Mg⁺², Al⁺³, Fe⁺², Fe⁺³, Cr²⁺, Cr³⁺, Ru²⁺, Ru³⁺.

EXAMPLE 1

In order to study the performance of NiAlF₅O(pyrazine)₂ for adsorptionof CO₂ and H₂S, a series of cyclables testing were carried out in a flowmode system using the sequence of tests described in FIG. 6.

NiAlF₅O(pyrazine)₂, a material from a related SiF₆ platform which isknown to be very selective to CO₂ was tested. Interestingly, the gasadsorption testings using CO₂/H₂S/CH₄:5/5/90 at 25° C. in TSR modeshowed a retention time in the column of 27 min/g for H₂S and CO₂,respectively (FIG. 7), indicative of similar affinity of theNiAlF₅O(pyrazine)₂ framework to both CO₂ and H₂S. These results showedthat H₂S and CO₂ could be removed simultaneously with the same affinity.

Most importantly, heating the adsorption column in a second TSR(temperature swing regeneration mode) cycle to 50° C. forNiAlF₅O(pyrazine)₂ did not significantly affect the retention time (25vs 27 min/g) for both H₂S and CO₂ respectively (FIG. 8).

FIG. 9 shows that TSR mode could be practiced for NiAlF₅O(pyrazine)₂using reactivation at 50° C. and even VSR mode at 25° C. with a minimumloss in the H₂S retention time while keeping the same affinity for H₂Sand CO₂. FIG. 9 shows that for NiAlF₅O(pyrazine)₂, the H₂S and CO₂uptakes were reduced by 20% between TSR and VSR (vacuum swingregeneration) mode when adsorption is carried at 50° C.

Finally, the reproducibility test (6th cycle) after 5adsorption-desorption tests showed that NiAlF₅O(pyrazine)₂ exhibit areproducible H₂S and CO₂ adsorption performance. In this case,NiAlF₅O(pyrazine)₂ can be utilized as a potential material for thesimultaneous removal of H₂S and CO₂.

EXAMPLE 2

With the exception of NiAlF₅O(pyrazine)₂, it was shown that other MOFmaterials studied exhibit higher selectivity and higher retention timefor H₂S than CO₂ at 25° C. (FIG. 10). Y-1,4-NDC-fcu-MOF is the bestmaterial from the studied materials for H₂S removal with retention timeof 70 min/gm (5% H₂S, 10 cm³/min flowrate). Retention time for H₂Sdecreases for almost 40% when temperature is increased to 50° C. (FIGS.11, 12), with highest retention time of 41 min/g (5% H₂S, 10 cc/minflowrate) for Y-1,4-NDC-fcu-MOF. Retention time of H₂S and CO₂ forY-1,4-NDC-fcu-MOF and Y-fum-fcu-MOF does not change during VSR at 25° C.(FIG. 13), while retention time for all the samples does not changeduring VSR at 50° C. (FIG. 14).

Unlike all other studied materials here, NiAlF₅O(pyrazine)₂ has the sameretention time of 28 min/gm (5% H₂S, 5% CO₂ 10 cm³/min flowrate) forboth H₂S and CO₂ at 25° C. (FIG. 10). By increasing temperature to 50°C., the retention time for CO₂ and H₂S only decrease slightly to 26min/gm (5% H₂S, 5% CO₂ 10 cc/min flowrate) unlike other materials (FIGS.11, 12). During VSR at 25° C. for NiAlF₅O(pyrazine)₂, the retention timefor H₂S decreases slightly (FIG. 13), however the retention time for H₂Sand CO₂ remains unchanged during VSR at 50° C. (FIG. 14).NiAlF₅O(pyrazine)₂ is a good candidate for simultaneous removal of H₂Sand CO₂ over the wide temperature range, while other studied materialscan be good candidates for removal of H₂S first and then CO₂ in thepresence of CH₄ containing gas streams at 25° C.

As shown in FIG. 15, uptake for all the materials remains practicallyunchanged between 1^(st) cycle and 6^(th) cycle under the same conditionshowing that all these materials selected for mixed gas testing are verystable.

The CO₂ and H₂S uptakes for all the MOFs studied in the course of thisproject, using TSR and VSR mode, are reported in Tables 1 and 2.

TABLE 1 Summary of H₂S and CO₂ adsorption uptakes of the best MOFs inTSR mode using CO₂/H₂S/CH₄ (5/5/90) Gas mixture (1 bar). CO₂ uptake H₂Suptake wt % wt % TSR mode TSR mode Materials 298 K 323 K 298 K 323 KGa-soc-MOF 0.58 0.39 3.11 1.74 Y-FTZB-fcu-MOF 0.98 0.78 3.30 2.04Y-1,4-NDC-fcu-MOF 1.18 0.74 5.31 3.14 Y-fum-fcu-MOF 0.78 0.49 3.94 2.58NiAlF₅(H₂O)(pyrazine)₂(solvent) 2.75 2.55 2.12 1.97 NiSiF6 DPA-i 1.571.32 3.94 2.27 *CH₄ uptake not detected by the flow mode system andCO₂/CH₄, H₂S/CH₄ selectivity is calculated assuming 0.1 mg as the lowestdetectable uptake

TABLE 2 Summary of H₂S and CO₂ adsorption uptakes of the best MOFs inVSR mode using CO₂/H₂S/CH₄ (5/5/90) at 1 bar Gas mixture (1 bar). CO₂uptake H₂S uptake wt % wt % VSR mode VSR mode Materials 298 K 323 K 298K 323 K Ga-soc-MOF 0.49 0.34 2.35 1.63 Y-FTZB-fcu-MOF 0.88 0.78 2.952.04 Y-1,4-NDC-fcu-MOF 1.18 0.78 5.16 3.19 Y-fum-fcu-MOF 0.78 0.59 3.872.58 NiAlF₅(H₂O)(pyrazine)₂(solvent) 2.45 2.55 1.78 1.97 NiSiF6 DPA-i1.76 1.32 3.49 2.28

Because if the low uptake of CH₄ vs H₂S and CO₂ during the mixed gastests, it was impossible to detect and quantify the CH₄ uptake for allthe studied materials. Accordingly, in order to determine the CO₂/CH₄ mdCO₂/H₂S selectivity (Tables 3 and 4), it was assumed that thenon-detectable uptake of CH₄ is equal the accuracy of the set-up (0.1mg).

TABLE 3 Summary of CO₂/CH₄ and H₂S/CH₄ adsorption selectivitiesdetermined for the best MOFs in TSR mode using CO₂/H₂S/CH₄ (5/5/90) at 1bar Gas mixture (1 bar). CO₂/CH₄ H₂S/CH₄ Selectivity* Selectivity* TSRmode TSR mode Materials 298 K 323 K 298 K 323 K Ga-soc-MOF 385 257 26351478 Y-FTZB-fcu-MOF 642 514 2796 1735 Y-1,4-NDC-fcu-MOF 771 482 45002667 Y-fum-fcu-MOF 514 321 3342 2185 NiAlF₅(H₂O)(pyrazine)₂(solvent)1800 1671 1800 1671 NiSiF6 DPA-i 1028 867 3342 1928 *CH₄ uptake notdetected by the flow mode system and CO₂/CH₄, H₂S/CH₄ selectivities arecalculated assuming the uptake of CH₄ is equal to 0.1 mg, which is thelowest detectable uptake by the set-up.

TABLE 4 Summary of CO₂/CH₄ and H₂S/CH₄ adsorption selectivitiesdetermined for the best MOFs in VSR mode using CO₂/H₂S/CH₄ (5/5/90) at 1bar Gas mixture (1 bar). CO₂/CH₄ H₂S/CH₄ Selectivity* Selectivity* VSRmode VSR mode Materials 298 K 323 K 298 K 323 K Ga-soc-MOF 321 225 19921382 Y-FTZB-fcu-MOF 578 514 2507 1735 Y-1,4-NDC-fcu-MOF 771 514 43712700 Y-fum-fcu-MOF 514 385 3278 2185 NiAlF₅(H₂O)(pyrazine)₂(solvent)1607 1671 1510 1671 NiSiF6 DPA-i 1028 867 3342 1928 *CH₄ uptake notdetected by the flow mode system and CO₂/CH₄, H₂S/CH₄ selectivities arecalculated assuming the uptake of CH₄ is equal to 0.1 mg, which is thelowest detectable uptake by the set-up.

Overall, all the materials selected exhibit very high selectivity forH₂S vs CH₄. As expected, the NiAlF₅O(pyrazine)₂ exhibited the highestselectivity for CO₂. It is noted that adsorption selectivity valueshigher than 700-1000 are often attached with elevated degree ofinaccuracy, hence, this values should be considered as infinite.Accordingly, the high values for CO₂/CH₄ and H₂S/CH₄ selectivitiesreported in tables 3 and 4 are highly qualitative.

In summary, highly stable recyclable MOF materials for H₂S and CO₂removal from natural gas with a wide range of H₂S/CO₂ selectivity aredescribed that can be used for TSR and VSR at room and highertemperatures. Highly selective materials are shown for CO₂ having openmetals sites (such as NiAlF₅(H₂O)(pyrazine)₂(solvent)) that have thepotential to remove CO₂ and H₂S simultaneously with high selectivity.

What is claimed is:
 1. A method of capturing chemical species from afluid composition, comprising: contacting a metal organic framework offormula [M_(a)M_(b)F_(6-n)(O/H₂O)_(w)(Ligand)_(x)(solvent)_(y)]_(z) witha fluid composition including at least carbon dioxide and hydrogensulfide; and capturing carbon dioxide and hydrogen sulfide from thefluid composition; wherein M_(a) is selected from Zn²⁺, Co²⁺, Ni²⁺,Mn²⁺, Zr²⁺, Fe²⁺, Ca²⁺, Ba²⁺, Pb²⁺, Pt²⁺, Pd²⁺, Ru²⁺, Rh²⁺, Mg²⁺, Al⁺³,Fe⁺³, Cr²⁺, Cr³⁺, Ru³⁺, and Co³⁺; wherein M_(b) is selected fromperiodic groups IIIA, IIIB, IVB, VB, VIB, and VIII; wherein the Ligandis a polyfunctional organic ligand, and x is 1 or more; wherein n is 1,w is 1, x is 2, y is 0 to 4, solvent is a guest molecule, and z is atleast
 1. 2. The method of claim 1, wherein M_(b) is selected from Al⁺³,Ga³⁺, Fe⁺², Fe⁺³, Cr²⁺, Cr³⁺, Ti³⁺, V³⁺, V⁵⁺, Sc³⁺, In³⁺, Nb⁵⁺, and Y³⁺.3. The method of claim 1, wherein the Ligand comprises pyrazine,pyrimidine, pyridazine, triazine, thiazole, oxazole, imidazole,pyrazole, triazole, oxadiazole, thiadiazole, benzoxazole, orbenzimidazole.
 4. The method of claim 1, wherein the metal organicframework includes open metal sites.
 5. The method of claim 1, whereincapturing comprises physical adsorption, chemisorption, or both physicaladsorption and chemisorption of the one or more captured chemicalspecies by the metal organic framework.
 6. The method of claim 5,wherein the metal organic framework includes one or more open metalsites and wherein chemisorption occurs by one or more captured chemicalspecies chemically interacting with one or more open metal sites of themetal organic framework.
 7. The method of claim 1, wherein the fluidcomposition further comprises water, methane, or both water and methane.8. The method of claim 1, further comprising desorbing carbon dioxideand hydrogen sulfide.
 9. The method of claim 1, further comprisingchanging the pressure, temperature, or both pressure and temperature ofthe capture environment to alter the affinity of one or more of carbondioxide and hydrogen sulfide for the metal organic framework adsorbent.10. The method of claim 1, wherein carbon dioxide and hydrogen sulfideare captured from the fluid composition simultaneously.